Choosing your keywords for you ad is very important. Google provides the following examples to demonstrate how you can select the most effective keywords for your campaigns.

 

From the Google Adwords site:

 

Remember that the more specific phrases are always better than general keywords. And a short, well-targeted list of words is much better than a long list of general keywords. We've found that our most successful advertisers use a combination of the following four types of keyword matching options:

• Broad matching example

Keyword: breast cancer
If you enter your keyword without any formatting, the AdWords program keyword default is broad match. For example, if your keyword were breast cancer, your ad would show when a Google search includes the keyword breast cancer, regardless of other search terms used or the order in which they were entered. Your ads will also automatically show for expanded matches, including plurals and relevant variations.

Broad match keywords can work very well when the keywords are specific to your organization. For example, here are search queries that might display an ad targeted to the broad match keyword breast cancer:

breast cancer information
cancer of the breast treatment
cancer support breast removal
cancer of the breast in men
support groups breast cancer
breast cancer symptoms
self breast exam to detect cancer

All of the queries above are related to breast cancer, and are therefore relevant. However, the broad match default doesn't work well for general keywords that may be included in searches unrelated to your organization, as in the next example.

Keyword: bears
An organization devoted to saving endangered bears should avoid the general keyword bears. Here are search queries that might display an ad targeted to the broad match keyword bears:

chicago bears
berenstain bears video
collectible teddy bears
bad news bears dvd

None of the searches listed above are relevant to the organization, yet they all include the keyword bear. Keywords such as grizzly bears and black bears would be a better option for the broad match default.
• Phrase matching example

Use quotes: "breast cancer"
If your keyword were "breast cancer", your ad would show when the keyword breast cancer is included in a search in that specific order. For example, your ad would show for breast cancer information, but not for cancer of breast information.

You can specify keywords as phrase matching by surrounding your keyword in quotes. In the broad match queries shown above, note that only the following searches would trigger the ad when breast cancer is entered as a phrase-matched keyword:

breast cancer information
support groups breast cancer
breast cancer symptoms

• Exact matching example

Use square brackets: [breast cancer]
If your keyword were [breast cancer], your ad would only show when a Google user searches on the keyword breast cancer. Your ad will not show if breast cancer research is searched.

You can specify keywords as exact matching by surrounding your keyword in square brackets. This technique works well for singular keywords, keywords that are general, or keywords that might have more than one meaning to a Google user.
• Negative matching example

Use a hyphen: -teddy
If your broad match keyword is bears and you don't want your ad to show for teddy bears, add the negative keyword -teddy.

You can specify keywords as negative matching by preceding an unwanted keyword with a hyphen. This technique works to limit the display of your ad on broad-match searches that don't apply to your organization. For example, if our endangered bear organization wanted to run on the broad-match keyword bear, the following negative keywords should be listed to avoid showing on unrelated queries:

-chicago
-berenstain
-bad news
-teddy